Melting copper



9, 1941. P. M. HULME E-rAL 2,265,284

V MELTING COPPER Filed Oct. 26, 1940 3 Sheets-$11961'l 1 ATTORN EYS EN.fm

i. M. HULME lrrm.v

MELTING COPPER Filed 0G11. 26, 1940 3 Sheets-Sheet 2 am. www D Tad. l mNH, R E O WX n 9, 1941. P. M. HULME ETAL MELTING COPPER 3 sheets-sheet:s

Fileaoct, 26, 1940 4 5 a 5 .Q um bo Rf, MY wuwk why M ,o WM. n A @Mm n,gm. @d Il Pom.

` and remains in the molten copper.

Patented Dec. 9, 1941 MELTING COPPER Philip M. Hnlme and Robert A.Ghelardi, Metuchen, N. li., assignors to International Smelting &Refining Company, a corporation vof Montana Application October 26,1940, Serial No. 362,956

6 Claims.-

This invention relates to the melting of cathode copper, and has for itsobject the provision of an improved method of melting such copper toproduce substantially. oxygen-free 'molten copper. The substantiallyoxygen-free molten copper resulting from the practice of the inventionmay be used tov produce any desired shapes (i. e. bars, billets, cakesetc.) of cast ycopper for subsequent fabrication, and the cast coppermay be substantially oxygen-free, flatset or tough-pitch, 'phosphorcopper orU other copper alloy, as desired.

Most of the copper commercially produced at the present time iselectrolytically refined. While commercial electrolytically refinedcopper (cathode copper) is usually very pureand substantially free ofoxygen, no commercially practical method has heretofore been availablefor melting such copper in a fuel-fired furnace without contaminatingthe melted copper with oxygen or other impurity or both. The presentin-v vention provides a method of melting cathode copper withoutcontamination in a fuel-fired furnace, and permits the production ofeither oxygen-free or nat-set copper castings (the latter by controlledincorporation of oxygen in the molten copper), as well as the productionof copper alloy castings such as phosphor copper casting them intoblocks. Whether or not the poling operation has proceeded to asuflicient extent is determined by observing the nature of the set or.pitch, that is the condition' or the exposed surface of these castsamples upon cooling. When the samples show a proper set, poling isstopped and the molten copper `is cast into suitable shapes.

and the like, without resort to the refiningy procedures heretoforefound necessary.

The heretofore customary practice for melting and casting cathode copperfollows generally the old Welsh process for fire-refining. It involvesfirst melting the copper in a fuel-fired furnace, skimming any slagformed, oxidizing the molten charge, skimming the oxidized iml purities,and then poling the charge to reduce cuprous oxide. -During the meltingoperation the copper is in contact with the gaseous combustion productsof the fuel, and some of these gases are absorbed in the and contaminatethe copper. To remove these contaminants and other impurities, themolten copper is blown with air and then skimmed. In this mannerimpurities in the copper are largely removed, but some copper oxide isunavoidably formed The molten copper, therefore, is next covered withcoke'and subjected to a poling operation' by plunging wooden poles belowthe surface of the molten metal. As a result 'of this operation, thecuprous oxide in the molten metal is reduced and the metal isconditioned yfor casting.

The progress of the poling operation is care-A fully Watched by takingfrequent samples and `The cast copper solidifying in the mold with asubstantially at or slightly crowned surface is known as tough-pitch orflat-set copper. This copper invariably contains a small amount ofoxygen (0.01 to 0.05%), since the presence of a small amount of oxygenis necessary to `nsure the flat-set desired for rolling and drawingoperations. The precise manner in which the oxygen functions to producea flat-set is not I'uiiy understood, but it is generally believed thatthe oxygen reacts with very small amounts of impurities (particularlysulphur) present even in cathode copper, and forms a gas, which comesout of solution as the copper cools. This gas expands and counteractsthe tendency of the copper to shrink upon freezing by forming minutecavities in the casting in suiiicient amount to prevent the formation ofa shrinkage cavity or pipe If insufficient gas is evolved. the surfacewill be depressed, or if too much gas is evolved, they surface will riseand may even be broken by y'a spew of metal forced through the frozensurface scum. The former is known as low-set copper and the latter asapplied to any copper containing this amount of oxygen, for in somecases (depending upon the amounts of impurities, such as sulphur, in thecopper) the presence of oxygen within these limits will not produce theflat-set or slightly crownedset required for commercial purposes.

' The melting and casting of cathode copper in fuel-firedfurnacesrequires the close attention and careful control of experiencedand skilled operators, particularlyduring the poling operation.Furthermore, the practice hasv the further disadvantage of being a batchoperation. Each furnace charge must be melted, oxidized and poled beforecasting vcan commence, so that the actual casting period, during whichthe furnace is producing a marketable product, is a small fraction ofthe time required for each cycle of theJ operation. In the case of thecustomary twenty-four hour cycle, for example, casting proceeds for onlyabout five hours.- A- stillprovements of a mechanical nature forlightening the manual work involved, these attempts lhave beencommercially unsuccessful and the general technique of the mainedunchanged.

-Molten copper containing oxygen may be deoxidized by suitable metallicdeoxidizing agents, such as phosphorus, silicon, calcium, lithium etc.The use of such deoxidizing agents is usually objectionable because theamount required for deoxidation of the copper is such that some of thedeoxidizer remains in the copper and lowers practice has long reitselectrical conductivity. Thus, for example,4

phosphorus deoxidized copper usually contains from 0.015 to 0.025%phosphorus. However, for certain uses this small amount of phosphorus isconsidered advantageous, in addition to evidencing complete deoxidationof the copper.

Oxygen-free copper of high electrical conductivity possesses certaindesirable properties for a number of uses, but its production byprocesses now availableis expensive, and consequently the commercialdemand for such oxygen-free copper is limited. Suclr oxygen-free copperhas heretofore been produced in electric melting furnaces, and bysubjecting molten copper, meltedv and refined as hereinbefore described,to a special deoxidizing treatment by bringing it into intimate contactwith charcoal.

The present invention contemplates an improved method of melting cathodecopper for producing substantially oxygen-free molten copper, which maybe cast as such, or may be used to produce flat-set cast copper shapes,phosphor copper and other copper alloys. In accordance with theinvention, the cathode copper. is melted lin the melting chamber of afuel-fired muilie furnace under conditions inhibiting the presence ofslag on the surface of the resulting molten copper, while maintainingin-the melting chamber above the molten copper therein a gaseousreducing atmosphere free of any constituent l, capable under theoperating conditions prevailing within the melting cham-ber ofdeleteriously affecting the molten copper. A bath of substantiallyyoxygen-free molten copper is maintained in the melting chamber underconditions permitting unhindered transfer of radiant heat to the surfacethereof. In other words, no medium of relatively poor heat conductivity,sucliv as slag, charcoal and the like," covers the surface of the moltenmetal andimpedes the transfer of radiant heat.- thereto. Preferably,Athe gaseous 'atmosphere within the melting chamber consists principallyof carbon monoxide and nitrogen, and may advantageously be derived byappropriate treatment of exhaust combustion )its incorporation in thebath of molten copper.

IThe melting operation is carried out continuously by maintaining asubstantially uniform volume of molten copper in the melting chamber andsuitably correlating the amount of cathode copper introduced into thechamber for melting with the amount of molten copper withdrawn from thechamber. Substantially oxygen-free molten copper is withdrawn from themelting chamber, and may be cast into shapes of substantiallyoxygen-free copper by withdrawing the molten metal and casting underconditions inhibiting the inclusion of oxygen in the resulting castshapes. By the controlled incorporation of oxygen in the substantiallyoxygen-free molten copper withdrawn from the furnace, flatset coppercastings may be produced. Phosphorus or other alloying metal may beincorcopper withdrawn from the furnace to produce phosphor copper andthe like.

The invention will be better understood from the following description,taken in conjunction with the accompanying drawings, in which Fig. 1 isa longitudinal sectional elevation of a fuel-nred muiile furnace adaptedfor the practice of the invention,

Fig. 2 is a sectional detail of the mechanical seal for the enteringcopper cathodes,

Fig. 3 is asectional elevation, taken on the section line 3 3- of Fig.1, showing the molten copper discharge launder and pouring ladle,

l ',Fig. 4.is a sectional plan of the launder and ladle shown in Fig. 3,

. Fig. 5 is a sectional detail taken on the section line 5-5 of Fig. 4,and y Fig. 6 is a ydiagrammatic flow sheet of the equipment forproviding the reducing gas required in the practice of the invention.

The furnace shown in the drawings has side walls III and II, end wallsI2 and I3, a oor or hearth I4 and an arched roof I5, all of refractorybrick. The interior of the furnace is divided into a 'melting chamber I6 and a combustion chamber I'I by ankarch I8 sprung between the sidewalls of the furnace. The arch I8 is relatively thin and of highrefractory material possessingv good heat-conducting properties, suchfor example as silicon carbide. The arch should be as thin as it ispractical to make it in order to permit maximum heat transfertherethrough. Silicon carbide (particularly that commercially known ascarbofrax) is mechanically strong, highly refractory and possessesrelatively good heat'conducting properties.

Oil' burners I9 extend through each of the end walls I 2 and I3 into thecombustionchamber II. The side wall I0 has near its center a flue 20 forthe withdrawal of combustion gases from the combustion chamber. Each endwall I2 and I3- has a charge opening 2| for introducing the coppercathodes to be melted into the melting 22 is provided for advancing thelowermost copper cathode of the pile or stack of cathodes 23 along adownwardly inclined floor 24 towards the charge opening 2|. lie end toend on the floor 24 and are advanced or fed at predetermined timeintervals towards and into the melting chamber I6 by the advance orfeeding of the lowermost cathode in the stack 23.

The melting chamber I6 has a tap hole 29, for the withdrawal of moltenmetal, approximately in the center of the side wall Il. A curtain wall30, at ythe inner end of the tap hole,

directs the molten metal into a discharge well 3l, and provides apositive molten metal seal for the melting chamber. The tap hole 29communicates with and discharges into a covered launder 32 for conveyingthe molten metal to a tilting casting ladle 33.

The launder 32 is built of suitable refractory material, such as clay,and is effectively insulated to prevent freezing of the molten copperflowing therethrough. A heating chamber 34 overlays the top of thelaunder and is separated fromthe launder by a thin layer of siliconcarbide rtile 35 (Figs. 4 and 5). The heatingchamber has at one end afuel burner opening 36 and at the other end a ue 31 communicating with astack 38 for the exhaust combustion gases.

A mechanical seal is provided to prevent air entering the meltingchamber I6 through the charge openings 2|. This seal comprises a pipe 25appropriately secured to the outside of the furnace structure adjacentthe charge opening 2I (Fig. 2). A longitudinal segment is' cut from thelower part of the pipe 25 to provide a slot 26 therein extending acrossthe Width of the charge opening. A plurality of contacting thin metalwashers 21, of larger diameter than the width of the slot 26, arepositioned for the most part within the pipe 25 and are operatively heldin position by the longitudinal edges of the slot 26. A fixed pipe 28extends through the washers 21 and prevents any accidental dropping ofthe washers. The washers are free to move vertically a certain distanceand thus conform across, the entire width of the charge opening 2l withany surface irregularities on the face of the copper cathodes.

The cylindrical tilting ladle 33 has at one end a feed tube 39 incommunication with the discharge end of the launder. 32 throughout theoperative tilting movement of th'e ladle. The communicating openings ofthe launder 32 andthe feed tube 39 are enclosed by a sealing hood 40havingan observation window 4I. A normally covered funnel 42 projectsthrough the top of the hood 4I) directly above the feed tube 39. Thefeed tube 39 extends below the surface of the molten copper in the ladle33. The ladle is tilted through a small angle for pouring and moltencopper ows over a discharge lip 43. In Figs. 3 and 4 of the drawings,the ladle 33 is shown casting molten copper into a vertical mold 44, thepouring and casting being carried out under a protecting hood'45.

Reducing gas is introduced into the melting chamber I6, above the moltencopper therein, through two pipes 46 on opposite sides of the tap hole29 (Fig. 4). The pipes 46 are connected by a pipe 41 to the reducing gassupply main 48. Pipesr 49 and 50, connected to the main 48, supplyreducing gas to the interior of the hoods 40 and45', respectively (Fig.3). Reducing gas Several cathodes 23 face of the molten copper in tureis derived by treatment of the exhaust com.-

bustion gas from the furnace. A certain amount of the combustion gas iswithdrawn from the fiue 20 through a pipe 5I and a water chamber 52 by apump 53 (Fig. 6). The cooled gas is forced through a water spray tower54 for the removal of sulphur dioxide and vthen through an iron oxidetower 55 for the removal of hydrogen sulphide. The thus-purified gasnext passes through a moisture trap 56 into an electrodryer 51. Such anelectrodryer may be of the type known by the trade-name Lectrodryer andmanufactured by the Pittsburgh Lectrodryer Corp., Pittsburgh,JPennsylvania.. The electrodryer is filled with activated alumina, andtwo are provided so that one may be regenerated while the other is inuse. The purified and dried gas, consisting now principally of carbondioxide and nitrogen, next passes through an. electrically heatedcharcoal reducer 58 where the carbon dioxide is reduced to carbonmonoxide. Two reducers 58 are provided so that one may be refilled withcharcoal while the other is in use. After passing through a filter 59the reducing gas mixture flows into the supply main 48. The supply mainmay of course include a gasometer for storage of the reducing gasmixture, 4Where irregularities in the production of or demandfor thereducing 'gas make its direct supply to the melting chamber and theprotecting hoods impracticable.

In practicing the invention in the apparatus shown in the drawings, thefurnace is fired by the oil burners I9 to heat the melting or muifiechamber I6 above the melting point of copper. The melting chamber isheated largely by radiant heat from the silicon carbide arch I8, and toa lesser extent by heat conducted through the side and end walls of thefurnace. Pure copper melts at a temperature of about 1980 F., but forpractical purposes the molten copper should be heated to a temperatureof about 2050 F. for satisfactory casting. vIn order to vmaintainanadequate melting rate in the'furnace for economic commercial operation,a temperature approximating 2500 F. should .preferably be maintaineddirectly beneath the arch I8.

Since the copper in the melting chamber I6 is heated largely by heatradiated to it from the under surface of the arch, it is important toestablish and maintain conditions favoring the transfer of radiant heatto the copper.

To this end, the surface of the molten copper shouldl possess highemissivity. In a sense this emissivity is a measure of the capacity ofthe molten copper to absorb the heat radiated to it. The emissivity ofmolten copper is adequately high to insure melting of the coppercathodes at .the desired rate when the temperature at the under surfaceof the arch I8 approximates 2500" F.

Fused slags generally possess higher emmissivity than molten copper, butthey are poor conductors of heat. If present on the surface of themolten copper, they impede `rather than aidin the transfer of radiant'.Aheat to the copper. Accordingly, "in practicing the invention, thesurthemelting chamb` er is maintained free of` slag, and to this end thecopper cathodes are melted under conditions inhibiting the formation ofslag and hence inhibiting the presence of slag on the surface of themolten copper.

Molten copper substantially free of oxygen or oxides exerts practicallyno effect upon common and inexpensive silica refractories, so that suchrefractories may be employed for the linings of the melting chamber.Many fused reactive slags vigorously attack silica refractories, so thatthe presence of such slags on the surface of the molten copper, whileaccomplishing no useful purpose in the practice of the invention, wouldnecessitate the use of expensive refractories to avoid serious damage tothe lining of the melting chamber.

It has heretofore been proposed to deoxidize molten copper bymaintaininga layer of charcoal on the surface thereof. Such a layer of charcoalwould perform no useful purpose inthe practice of the present invention,and would moreover be objectionable since its relatively poor heatconductivity would impede the transfer of radiant heat to -the moltencopper. The presence of charcoal on the surface of the molten copper isapt to be attended by the further disadvantage of coating the under-sideof the arch I8 with a lm of finely divided charcoal which mayobjectionably decrease the heat conductivity of the arch. h

While the surface of the molten copper in the melting chamber is free ofslag and of any other medium impeding the transfer of radiant, heatthereto, oating patches' of unfused or partially fused refractorymaterial may gather on the surface of the moltencopper. Where themelting chamber is lined with silica brick, these floating patchesconsist mainly of silica and appear to be due to mechanical erosion ofthe lining by the molten copper. 'I'his has been observed to occur to asmall extent in a newly-lined furnace when .it is rst put in operation.So long as these floating patches cover in the aggregate only a smallpart of the surface of the molten copper,

they are of no practical significance. However, they should be raked orpulled olf the surface of the molten copper from time to time, in orderto insure elcient transfer of radiant heat to the surface of the moltencopper aswell as eective direct exposure of the surface of the moltencopper to the gaseous reducing atmosphere.

A bath of substantially oxygen-free molten copper is maintained in themelting chamber I6. The level of this bath of molten copper isdetermined by the height of the overowof the discharge well 3| into thelaunder 32. A gaseous reducing atmosphere is maintained above thesurface of the molten copper in the melting chamber I6. In the apparatusof the drawings,

this gas is supplied to the melting chambervv through the pipes 46 andconsists principally of carbon monoxide and nitrogen and is derived bytreatment of exhaust combustion gas from the furnace as hereinbeforedescribed. The pressure of the reducing gas atmosphere within themelting chamber I6 is slightly higher than the atmospheric pressure (e.g. around IAO@ of an inch of water) thus insuring against the entranceof air and combustion gases into the chamber. 'I'he reducing gas escapesfrom the melting chamber through cracks in the furnace structure andthrough the charge openings 2 I.

While it is our preferred practice to obtain the reducing gas mixture bytreatment of exhaust combustion gas.'other sources may be availed 'ofducer gas consisting predominantly of carbon monoxide and nitrogen issuitable. The reducing gas mixture should be free of any constituent'capable under the operating conditions prevailing within the meltingchamber of deleteriously affecting the oxygen-free molten copper.presence of hydrogen in the reducing gas mixture should be avoided,since hydrogen is readily absorbed by molten copper and adverselyaffects the set of copper upon casting. Even the presence of a smallamountv of water vapor is ob# jectionable, since at the temperatureprevailing in the melting chamber water vapor decomposes into hydrogenand oxygen (particularly in the presence of carbon monoxide) and theresulting hydrogen may adversely affect the set of the copper duringcasting.

The reducing gas mixture should be reasonably free of carbon dioxide,since carbon dioxide l reacts with molten copper to yield carbonmonoxide and cuprous oxide. A small amount of carbon dioxide in thepresence of a large amount of v mation of cuprous oxide is for mostpractical v purposes sufficiently retarded.

'I'he presence of decomposable hydrocarbons in the reducing gas,atmosphere in the melting chamber is undesirable, since suchhydrocarbons are cracked at the prevailing temperature-and carbon isdeposited on the surfaceof the metal or on the under-surface of the archor on both. Such deposits of carbon,`whether on thesu'rface of the metalor on the under-surface of the arch, materially lower the melting rateof the-furnace by impeding the transfer of radiant heat to the moltencopper. The illuminants present in coal gas or any enriched-producer gasor"water gas such as is available in most cities are examples ofdecomposable hydrocarbons which behave in this manner.

It is also desirable to avoid the presence of sulphur in the gaseousreducing atmosphere in the melting chamber. Some sulphur (usually in theform of copper sulphate or sulphuric acid occludedin the cathode) isunavoidably introduced yinto the melting chamber with the charge. The

molten copper. to produce the desired set of tough-pitch copper, ashereinbefore explained.

.The copper charged into the melting chamber usually contains as muchsulphur as is desirable, and therefore the presence of sulphur orsulphur compounds in the gaseous reducing atmosphere of the meltingchamber should usually be avoided.

The hooks of the initial starting sheets of the copper cathodes arepreferably cut off before charging the cathodes into the meltingchamber. Undesirable amounts of oxidized copper, copper sulphate etc.are frequently associated with these hooks and it is hence better not toattempt to melt them in practicing the present invention. The cathodesare stacked (23) and automatically fed into the melting chamberalternately by the two sheet-feeding devices (22) at the opposite endsof the furnace. The plus pressure of the gaseous reducing atmospherewithin-the melting chamber and the mechanical seal alongside the chargeopening 2| effectively prevents the introsheet-feeding device operatesat 8 minute intervals. The preheating of the cathode for this intervalof 8 minutes in contact with the gaseousY reducing atmosphereeffectively reduces any copper oxide on its surface, and substantiallyinsures the absence of oxygen on or within the cathode when it isultimately pushed off the feeding floor into the bath of `molten copper.Whatever slight amount of ozidized copper that may be introduced intothe bath of molten copper during charging and melting of the cathodes isreadily reduced by the gaseous reducing atmosphere, so that the" bath'of molten copper maintained continuously in the melting chamber I6 isfor all practical purposes substantially oxygen-free.

The apparatus illustrated in the drawings is adapted for the productionof castings of substantially oxygen-free copper of high electricalconductivity. The reducing gas mixture is supplied to the hoods 40 and45 so that the substantially oxygen-free molten copper withdrawn fromthe melting chamber is not allowed to come in contact with air or otheroxidizing influence while flowing down the launder 32 or while in theladle 33 or during casting.

In practicing the invention for the production of tough pitch copper,the removable covers E@ of the heating chamber 34 and the covering tiles35 for the launder 32 are removed, or the launder structure is replacedby a substantially open launder. The moltenlcopper flowing through theopen launder is covered with a layer of charcoal -toprevent it frombecoming oxidized to anundesirable extent, but the coverage of thecopper by the charcoal is incomplete, so as to` permit the copper to beexposed to the air sufficiently presence of air currents in the vicinityof the.

launder, influence the amount of oxygen absorbed by the molten copper asit flows through the launder. Other variable factors, such as the amountof sulphur present in the copper, alect easier of control in thepractice of the invention than it is in the poling operation of theprior art refining practice.

The molten copper, with its oxygen content controlled as just described,flows into-the tilting ladle 33, which need not for this operation beprovided with the hood 45. If necessary or desirable, the ladle may beheated by an oil flame through the end opening Bl. It has been foundthat contact of the molten copper with combination gases in a oil heatedladle is not objectionable, apparently because the molten 4copperre'mains in the ladle for too short a period of time to becomecontaminated by the gases.

Copper alloys, such as phosphor copper or silicon copper, may Lbeproduced by adding controlled amounts of the alloying metal to thesubstantially oxygen-free molten copper Withdrawn from the meltingchamber. Such alloying metals are preferably added to the molten copperin'the ladle just before casting, as for example through the normallycovered funnel 42. Alloying metals may be similarly added to the moltencopper in the ladle after the controlled incorporation of oxygentherein, as hereinbefore described. l

While the copper cathodes are charged periodically, at predeterminedshort time intervals, the melting and casting operation is for allpractical purposes continuous; substantially oxygenfree molten copperbeing withdrawn from the melting chamber at substantially the same rateas the cathodes are charged. The substantially oxygen-free molten copperdoes not affect the refractory lining of the melting chamber, and no slagis present to attack the lining. The furnace is not repeatedly heatedand cooled, as heretofore customary in melting copper cathodes, and thefumace refractories are hence not subject to thermal shock.

Aside from the usually minute amount of oxidized copper present on the.surface of copper 1 cathodes, the method of the invention removes noimpurities. from the copper. But the method of the invention doeseffectively reduced whatever amount 'of oxidized copper is ordinarilyassociated with the copper cathode. The surface of the molten copper isexposed tothe direct influence of the gaseous reducing atmosphere theamount of oxygen required to produce a fiat-set' upon casting andcooling. Accordingly, it is not possible to formulate precisely whatproportion of the surface of the molten copper flowing through thelaunder should be exposed to the air. This can be determined, however,by the usual procedure of casting small test blocks and observing theset thereof upon solidifying. If the set indicates that too much oxygenis present in the copper, additional charcoal is added to the launder,or if the set indicates a deficiency of oxygen, some 4of the charcoal israked from the surface of the molten copper in the launder. About 0.01to 0.05% oxygen by Weight should be .incorporated in the copper toobtain the desired flat-set. Although the test here employed is the sameas that used in the heretofore customary rei'lning practice, the amountof oxygen ultimately incorporated in the molten copper is very much andany cuprous oxide in the molten copper is thereby reduced. Such cuprousoxide tends naturally to migrate to the surface of the molten copper,and this tendency is promoted by the agitation of the molten copper asthe cathodes drop into the molten copper alternately from the two endsof the melting chamber. In addition to copper cathodes, other forms ofequally pure substantially oxygen-free copper may constitute all or partof the copper charged into the melting chamber. Where, in the productionof tough-pitch cast copper, insufficient sulphur is present in thecathodes to be melted, a controlled amount of sulphur may beincorporated in the molten copper in the melting chamber, as for exampleby the controlled introduction of sulphur dioxide gas or by the additionof elemental 'sulphur along with the cathodes as charged into themelting chamber.

We-claim: f'

1. The method of melting cathode copper which comprises heating themelting chamber of a fuel-fired muflie furnace to a temperature abovethe melting point of copper, maintaining a bath of substantiallyoxygen-free molten copper in said melting chamber, the surface ofsaidbath of molten copper being free of slag and of any other mediumimpeding the transfer of radiant heat thereto, maintaining in themelting chamberV above the molten copper therein a gaseous reducingatmosphere free of any constituent capable under the operatingconditions prevailing within the chamber of deleteriously affecting theoxygen-free molten copper, introducing the cathvfired muilie furnace toa temperature above the melting point of copper, maintaining a bath ofsubstantially oxygen-free molten copper in said melting chamber, thesurface of said bath of` molten copper being free of slag and charcoal,maintaining in the melting chamber above the molten copper therein agaseous reducing atmosphere free of any constituent capable under th'eoperating conditions prevailing within the chamber of deleteriouslyaffecting the oxygen-free molten copper, introducing the cathode copperto be melted into the melting chamber under conditions substantiallyinhibiting the introduction of air into the chamber and melting thecopper so -introduced while maintaining the aforesaid slagandcharcoal-free bath of substantially oxygen-free molten copper, andwithdrawing substantially oxygen-free molten copper from the meltingchamber.

' 3. The method of melting cathode copper which comprises heating themelting chamber of a fuelred muiile furnace to a temperature 'above themelting chamber, the surface of said bath of substantially oxygen-freemolten copper in said meltingY chamber, the surface of said bath ofmolten copper being free of slag and charcoal, maintaining in themelting chamber above the molten copper therein a gaseous reducingatmosphere consisting principally of carbon monoxide and nitrogen,introducing the cathode' copper to be melted into the melting chamberunder conditions substantially inhibiting the introduction` of air intothe chamber and melting the copper so introduced while maintaining theaforesaid slagand charcoal-free bath of substantially` oxygen-freemolten copper, and withdrawing substantially oxygen-free molten copperfrom the melting chamber.

4. The method of melting cathode copper which comprises heating asilica-lined melting chamber of a fuel-firedmule furnace to atemperature above the melting point of copper, maintaining a bath ofsubstantially oxygen-free molten copper in said melting chamber, thesurface of said bath of molten copper being freel of slag and charcoal,maintaining in the melting chamber above the moltencopper therein agaseous reducing atmosphere consisting principally of carbon monoxideand nitrogen and free of any constituent capable under the operatingconditions `prevailing within the chamber of deleteriously affecting theoxygen-free molten copper, introducing the cathode copper to be meltedinto the melting chamber under conditions substantially inhibiting theintroduction of air into the chamber and melting the copper sointroduced while maintaining thel aforesaid slagand charcoal-free moltenbath of substantially oxygen-free copper, and withdrawing substantiallyoxygen-free molten copper from the melting chamber. Y

5. The method of melting cathode copper in a continuously operatedfuel-nred munie furnace which comprises heating the melting chamber ofthe furnace to a'temperature above the melting point of copper,maintaining a bath of substantially oxygen-free molten Icopper in saidmelting chamber, the surface of said bath of molten copper being free ofslag and charcoal, maintaining in the melting chamber above the moltencopper therein a gaseous reducing atmosphere free of any constituentcapable under the operating conditionsl prevailing within the chamber ofdeleteriously affecting the oxygen-free molten copper, introducing thecathode copper to be melted into the melting chamber under conditionssubstantially inhibiting the introduction of air into the chamber andmelting the copper so introduced while maintaining the aforesaid slagandcharcoal-free bath of substantially oxygen-free molten copper,withdrawing substantially oxygen-free molten copperfrom the meltingchamber, and maintaining a substantially uniform volume of molten copperin the melting chamber by correlating the amount of cathode copperintroduced into the chamber for melting with the amount of 'moltencopper withdrawn from the chamber.

6. The method of melting cathode copper to produce cast `shapes ofsubstantially oxygen-free copper which comprises heating the meltingchamber of a fuel-fired mufe furnace to a temperature above the meltingpoint of copper,

maintaining a bath of substantially oxygen-free molten copper in saidmelting chamber, the surface of said bath of molten copper being freelof slag and charcoal, maintaining in the melting chamber above themolten copper therein a gaseous reducing atmosphere free of anyconstituent capable under the operating conditions prevailing within thechamber of deleteriously affecting the oxygen-free molten copper,introducing the cathode copper to be melted into the melting chamberunder conditions substantially inhibiting the introduction of air intothe chamber and melting the copper so introduced while maintaining theaforesaid slag- 'and charcoalfree bath of substantially .oxygen-freemolten copper, and withdrawing from the melting chamber and casting`substantially oxygen-free molten copper under conditions inhibiting theinclusion of oxygen in the resulting cast shapes.

PHILIP M. HULME. ROBERT A. GHELARDI.

CERTIFICATE oE CORRECTION. Patent Np. 2,265,28h. December 9, 191m.-

PHILIP M. EUIME. ET AL.

I Itis hereby certified that error appears in the printed specification`of the above numbered patent requiring correction as followsz' Page l,first column, line lll, strike out "the" first occurrence; pagej, secondcolumn line 68- 69, v for "emmissiv-ity"read--emissivity-e; page '5,first column, line 18, for "ozidized" read "oxidized-; l-ine )4.7, for"incomporate". read '--incorporat e; and second column, line'll, for"combination gases in a oil read --combustion gases in an oil; line)4.5, for reduced read --reduce--gv page 6, first column, lineA )4.1,claim 5, for the words "melting chamber, the surface of'said bath of"read --nelting point of copper, maintaining a bath of; and secondcolumn, line l5, claim 5, for "muffie" read muffle; and that thesaidLetters Patent should be read with this correction therein that `thesame may conform tothe record of the case in the Patent Office.

Signed and sealed this 20th day of January, A. D. 19142.

. Y Henry Van Arsdale, (Seal) Acting Commissionerl of Patents.

